This invention relates generally to techniques for manufacturing semiconductor integrated circuits.
In the manufacture of semiconductor integrated circuits, a photoresist film is formed over a semiconductor wafer. The photoresist film may be irradiated so that some regions of the photoresist film are either harder or easier to remove. As a result, a pattern can be repeatedly transferred to the semiconductor wafer via the photoresist film. After developing, the photoresist film may be used as a mask for etching desired features in the underlying layers of the semiconductor wafer.
Advances in photolithography techniques utilized to transfer patterns to photoresist have enabled increasingly smaller patterns to be transferred. This means that smaller integrated circuit features can be formed in integrated circuits. As a result, more elements can be put in a given area on the semiconductor integrated circuit. One result of these advances has been to reduce the cost of integrated circuits.
Photolithographic advances have allowed progressively smaller irradiation wavelengths to be used. For example, deep or extreme ultraviolet wavelengths on the order of 190-315 nanometers may be used with chemically amplified photoresists. Chemically amplified photoresists use a photoacid generator and an acid sensitive polymer.
While advances in photolithography have been progressing at an impressive rate, other problems associated with photolithography have not been proceeding at a corresponding pace. One such issue arises with respect to line edge or line width roughness. Line edge or width roughness is roughness on the edge surfaces of the patterned photoresist. This roughness may be transferred to the underlying etched layers. When those etched layers form integrated circuit transistors, those transistors may have leakage problems.
In chemically amplified photoresist systems, photoacid generator diffusion during the post-exposure bake, as well as polymer chain non-uniformity, may result in line edge roughness problems. In other words, the diffusion of the photoacid generator during the post-exposure bake may continue to remove some portion of the photoresist outside the region which is defined by the pattern transferred to the photoresist.
Thus, it is desirable to reduce the roughness associated with the transfer of patterns to chemically amplified photoresist.